It depends. Young people (particularly girls) often say 'bitch' to their friends, as a joke. But if somebody you do not know calls you a bitch they are probably being very rude.

Yes, be offended. Unless it's a friend who calls you that as a joke, then it is an insult.

It can be used softly between friends but generally if someone said "you bitch" or referred to you as a bitch it is really bad.

If it has happened to you, you probably should be offended. In the U.S. someone calls a woman "a bitch" if they are angry, and think that the woman is aggressive, or mean, or too bossy, or complains a lot. I would never, ever, ever call my wife that word, not even as a joke. It depends who and when and the tone of voice. All kinds of insults _can_ sometimes be OK between friends, when said as a joke. "Bitch" literally means a female dog (perra). In addition to "mean woman," in English there is a _second_ set of "bad" meanings for "bitch." I think that "perra" in Spanish has some of these meanings, too: a prostitute, or a sexually subservient person. In the insult "son-of-a-bitch," often spoken aloud using the letters "SOB," "bitch" means prostitute, puta. It's a strange word because people who work with dogs use the word "bitch" normally in everyday speech, to mean simply a female dog. Therefore, "bitch" is not one of the worst words. It's not one of "the seven words you can't use on television."